This proposal requests support for the purchase of a fluorescence activated cell sorter (FACS) for use as share equipment at the State University of New York at Stony Brook (SUSB). The FACS will be primarily used to advance ongoing clinical and basic research projects. These projects include: 1) examining the effect of human immunodeficiency virus (HIV) infection on cellular characteristic both in vivo and in vitro; 2) examining novel cell surface molecules and isolating cell populations on the basis of their expression of these antigens including complement receptors such as C1q, cryoglobulins, and receptors on basophils and mast cells for cytokines inducing histamine release; 3) studying the biochemistry and kinetics of the uptake of cholesterol from LDL particles by macrophages; 4) investigating the nature of surface molecules expressed by cells of the developing nervous system and the role of carbohydrate moieties on these antigens in cell-cell adhesion; 5) examining lymphocyte subpopulations and their immunomodulatory role in various diseases; 6) studying the role of Epstein-Barr viral proteins in modulatin B cell function in vivo, and 7) isolating and cloning B cells of defined antigen and IgG subtype specificity to facilitate producing human monoclonal antibodies against HIV and other human pathogens. The current cell sorter facilities at SUSB are inadequate to support these research needs. The instrument required for these diverse projects must include 3-color capabilities, cloning capacity, microsampling attachments, a biocontainment feature, and sufficient processor capacity to allow multitasking with simultaneous accession of new data and analysis of previously acquired data. We are requesting the Becton-Dickinson FACStar-Plus which has the ability to perform the required operations. This instrument will accommodate the varying requirements of the primary user group and will represent an important research tool to many biomedical investigators at University.